The structure and processing of the small 1A protein of human respiratory syncytial virus (RSV) was investigated. The 1A protein accumulated intracellulary as four species: two species (4.8K and 7.2K) were unglycosylated and differed in length because translational initiation for the synthesis of the 4.8K species occurred at the second methionine in the sequence. The two other forms (13-15K and 21-30K) contained an N-linked carbohydrate side chain. The 13-15K species appeared to be converted into the 21- 30K form by the post-translational additional of polyactosamine to the N-linked side chain. This complex processing pathway for 1A was conserved between the RSV antigenic subgroups. All forms of 1A were shown to be inserted into intracellular membranes regardless of glycosylation status, and all forms except 4.8K were transported to the cell surface. Protein-mapping studies showed that the C-terminus of the 1A protein is extracellular, whereas the N-terminus is cytoplasmic. Additional studies to investigate the structure and processing of other RSV proteins are discussed.